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ring-buffer: Validate boot range memory events
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Make sure all the events in each of the sub-buffers that were mapped in a
memory region are valid. This moves the code that walks the buffers for
time-stamp validation out of the CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS
ifdef block and is used to validate the content. Only the ring buffer
event meta data and time stamps are checked and not the data load.

This also has a second purpose. The buffer_page structure that points to
the data sub-buffers has accounting that keeps track of the number of
events that are on the sub-buffer. This updates that counter as well. That
counter is used in reading the buffer and knowing if the ring buffer is
empty or not.

Link: https://lkml.kernel.org/r/20240612232026.172503570@goodmis.org

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineeth Pillai <vineeth@bitbyteword.org>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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Steven Rostedt (Google) committed Jun 14, 2024
1 parent c76883f commit 5f3b6e8
Showing 1 changed file with 152 additions and 38 deletions.
190 changes: 152 additions & 38 deletions kernel/trace/ring_buffer.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1675,10 +1675,152 @@ static bool rb_meta_valid(struct ring_buffer_meta *meta, int cpu,
subbuf = (void *)subbuf + subbuf_size;
}

pr_info("Ring buffer meta is from previous boot!\n");
return true;
}

static int rb_meta_subbuf_idx(struct ring_buffer_meta *meta, void *subbuf);

static int rb_read_data_buffer(struct buffer_data_page *dpage, int tail, int cpu,
unsigned long long *timestamp, u64 *delta_ptr)
{
struct ring_buffer_event *event;
u64 ts, delta;
int events = 0;
int e;

*delta_ptr = 0;
*timestamp = 0;

ts = dpage->time_stamp;

for (e = 0; e < tail; e += rb_event_length(event)) {

event = (struct ring_buffer_event *)(dpage->data + e);

switch (event->type_len) {

case RINGBUF_TYPE_TIME_EXTEND:
delta = rb_event_time_stamp(event);
ts += delta;
break;

case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
delta = rb_fix_abs_ts(delta, ts);
if (delta < ts) {
*delta_ptr = delta;
*timestamp = ts;
return -1;
}
ts = delta;
break;

case RINGBUF_TYPE_PADDING:
if (event->time_delta == 1)
break;
fallthrough;
case RINGBUF_TYPE_DATA:
events++;
ts += event->time_delta;
break;

default:
return -1;
}
}
*timestamp = ts;
return events;
}

static int rb_validate_buffer(struct buffer_data_page *dpage, int cpu)
{
unsigned long long ts;
u64 delta;
int tail;

tail = local_read(&dpage->commit);
return rb_read_data_buffer(dpage, tail, cpu, &ts, &delta);
}

/* If the meta data has been validated, now validate the events */
static void rb_meta_validate_events(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_meta *meta = cpu_buffer->ring_meta;
struct buffer_page *head_page;
unsigned long entry_bytes = 0;
unsigned long entries = 0;
int ret;
int i;

if (!meta || !meta->head_buffer)
return;

/* Do the reader page first */
ret = rb_validate_buffer(cpu_buffer->reader_page->page, cpu_buffer->cpu);
if (ret < 0) {
pr_info("Ring buffer reader page is invalid\n");
goto invalid;
}
entries += ret;
entry_bytes += local_read(&cpu_buffer->reader_page->page->commit);
local_set(&cpu_buffer->reader_page->entries, ret);

head_page = cpu_buffer->head_page;

/* If both the head and commit are on the reader_page then we are done. */
if (head_page == cpu_buffer->reader_page &&
head_page == cpu_buffer->commit_page)
goto done;

/* Iterate until finding the commit page */
for (i = 0; i < meta->nr_subbufs + 1; i++, rb_inc_page(&head_page)) {

/* Reader page has already been done */
if (head_page == cpu_buffer->reader_page)
continue;

ret = rb_validate_buffer(head_page->page, cpu_buffer->cpu);
if (ret < 0) {
pr_info("Ring buffer meta [%d] invalid buffer page\n",
cpu_buffer->cpu);
goto invalid;
}
entries += ret;
entry_bytes += local_read(&head_page->page->commit);
local_set(&cpu_buffer->head_page->entries, ret);

if (head_page == cpu_buffer->commit_page)
break;
}

if (head_page != cpu_buffer->commit_page) {
pr_info("Ring buffer meta [%d] commit page not found\n",
cpu_buffer->cpu);
goto invalid;
}
done:
local_set(&cpu_buffer->entries, entries);
local_set(&cpu_buffer->entries_bytes, entry_bytes);

pr_info("Ring buffer meta [%d] is from previous boot!\n", cpu_buffer->cpu);
return;

invalid:
/* The content of the buffers are invalid, reset the meta data */
meta->head_buffer = 0;
meta->commit_buffer = 0;

/* Reset the reader page */
local_set(&cpu_buffer->reader_page->entries, 0);
local_set(&cpu_buffer->reader_page->page->commit, 0);

/* Reset all the subbuffers */
for (i = 0; i < meta->nr_subbufs - 1; i++, rb_inc_page(&head_page)) {
local_set(&head_page->entries, 0);
local_set(&head_page->page->commit, 0);
}
}

static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages)
{
struct ring_buffer_meta *meta;
Expand Down Expand Up @@ -1757,8 +1899,6 @@ static void *rbm_next(struct seq_file *m, void *v, loff_t *pos)
return rbm_start(m, pos);
}

static int rb_meta_subbuf_idx(struct ring_buffer_meta *meta, void *subbuf);

static int rbm_show(struct seq_file *m, void *v)
{
struct ring_buffer_per_cpu *cpu_buffer = m->private;
Expand Down Expand Up @@ -2011,6 +2151,8 @@ rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
if (ret < 0)
goto fail_free_reader;

rb_meta_validate_events(cpu_buffer);

/* If the boot meta was valid then this has already been updated */
meta = cpu_buffer->ring_meta;
if (!meta || !meta->head_buffer ||
Expand Down Expand Up @@ -3955,11 +4097,10 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
struct rb_event_info *info,
unsigned long tail)
{
struct ring_buffer_event *event;
struct buffer_data_page *bpage;
u64 ts, delta;
bool full = false;
int e;
int ret;

bpage = info->tail_page->page;

Expand All @@ -3985,39 +4126,12 @@ static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
if (atomic_inc_return(this_cpu_ptr(&checking)) != 1)
goto out;

ts = bpage->time_stamp;

for (e = 0; e < tail; e += rb_event_length(event)) {

event = (struct ring_buffer_event *)(bpage->data + e);

switch (event->type_len) {

case RINGBUF_TYPE_TIME_EXTEND:
delta = rb_event_time_stamp(event);
ts += delta;
break;

case RINGBUF_TYPE_TIME_STAMP:
delta = rb_event_time_stamp(event);
delta = rb_fix_abs_ts(delta, ts);
if (delta < ts) {
buffer_warn_return("[CPU: %d]ABSOLUTE TIME WENT BACKWARDS: last ts: %lld absolute ts: %lld\n",
cpu_buffer->cpu, ts, delta);
}
ts = delta;
break;

case RINGBUF_TYPE_PADDING:
if (event->time_delta == 1)
break;
fallthrough;
case RINGBUF_TYPE_DATA:
ts += event->time_delta;
break;

default:
RB_WARN_ON(cpu_buffer, 1);
ret = rb_read_data_buffer(bpage, tail, cpu_buffer->cpu, &ts, &delta);
if (ret < 0) {
if (delta < ts) {
buffer_warn_return("[CPU: %d]ABSOLUTE TIME WENT BACKWARDS: last ts: %lld absolute ts: %lld\n",
cpu_buffer->cpu, ts, delta);
goto out;
}
}
if ((full && ts > info->ts) ||
Expand Down

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